The present invention relates to the inspection of the taper of the walls in a mold for continuous casting.
Molds for continuous casting of slab ingots are frequently constructed from individual plates which are mounted in a manner which permits adjustment of the dimensions of the mold cavity. The French Pat. No. 1,388,653 is representative of the state of the art of such molds, particularly as to the feature of providing each mold with a particular taper in down direction. The taper is adjusted by means of spindles, and the adjustment depends on the relative width-to height-to depth relation of the mold, on the brand or grade of steel and on the casting and ingot withdrawal speed. Choice of the proper taper is quite important and rather critical on the small sides of the mold. The ingot as cast tends to shrink particularly because the temperature drops generally in the direction of casting, and shrinkage along the long, traverse axes of the slab (in cross-section) is more pronounced than along the short axes.
It follows from the foregoing, that the taper of the mold wall plates has to be adjusted individually. One uses here a reference which is established by a plumb line (plummet, plumb bob, or the like) in order to ascertain the horizontal displacement of the lower edge from a vertical plane through the upper edge (or vice versa) of the wall. It was found that this kind of measurement is not too reliable and rather cumbersome. Other methods are known to measure the taper of a mold walls by scanning its inner surface.
The known methods for ascertaining the actual taper of a wall of a mold have the disadvantage that they require an empty mold, i.e. they can be practiced only when casting is not in progress. This reduces further the overall duty cycle time of a casting machine.
Investigations have shown that particularly the broad side walls of a mold for continuously casting slab ingots undergo a certain expansion which results in an uncontrolled displacement of the small sides, particularly under reduction of the taper thereof. This effect has been explained as being due to irregular expansion of different parts of a mold wall due to differences in thermal load. Since the parameters and conditions of casting remain the same otherwise, this change in taper has a detrimental effect on the quality of the cast ingot. Actually, the skin may even rupture due to such taper changes during casting.